Timber, Lime and Mortar Study Notes for Civil Engineering

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Timber, Lime and Mortar are the different building materials used to construct various civil engineering structures. They might be temporary structures or permanent structures. Generally, timber and other types of wood are used for the construction of temporary structures. The use of these building materials for civil engineering construction works depends on their properties, strength, availability and constituents.

Timber is a type of wood that exists naturally for construction. The strength and other quality parameters of timber depend on their constituents and the type of formation. This article contains basic notes on the “Timber, Lime and Mortar” topic of the “Building material” subject.

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What is Timber?

Timber is a type of wood used to construct civil engineering structures. It is generally used for the construction of temporary structures. Timber can be formed in any shape, like beams, planks, columns etc. The strength and classification of timber depending on the type of trees from which it is formed, So let’s understand the different types of trees.

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Classification of Trees

Trees are classified according to their mode of growth. The following chart shows the different types of trees. These types of trees are different from each other in terms of their formation and internal structure.


1. Exogenous Trees

  • Conifers are also known as evergreen trees, and the leaves of these do not fall till new ones are grown. As these bear cone-shaped fruits, they have been given the name conifers. These trees yield softwoods.
  • Deciduous trees are also known as broadleaf trees, and the leaves of these trees fall in autumn, and new ones appear in the spring season. Timber for engineering purposes is mostly derived from deciduous trees. These trees yield hardwoods.

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Comparison of Soft Wood and Hard Wood


2. Endogenous Trees

These trees grow inwards, and fibrous mass is seen in their longitudinal sections. Timber from these trees has very limited engineering applications. Examples of endogenous trees are bamboo, cane, palm, etc.

Structure of a Tree

From the visibility aspect, the structure of a tree can be divided into two categories:

1. Macrostructure

  • Pith: The innermost central portion or core of the tree is called the pith of the medulla.
  • Heart Wood: The inner annual rings surrounding the pith is known as heartwood. It is usually dark in colour.


  • Sap Wood: The outer annual rings between the heartwood and cambium layer are called sapwood.
  • Cambium Layer: The thin layer of sap between sapwood and the inner bark is known as the cambium layer.
  • Inner Bark: It gives protection to the cambium layer from any injury.
  • Outer Bark: It consists of cells of wood fibre and is also known as the cortex.
  • Medullary Rays: The thin radial fibres extending from the pith to the cambium layer are known as medullary rays.

2. Microstructure

  • Wood consists of living and dead cells of various sizes and shapes.
  • A living cell consists of four parts, namely (i) membrane, (ii) protoplasm, (iii) sap (iv) core. The cell membrane consists mainly of cellular tissue and cellulose. Protoplasm is a granular, transparent viscous vegetable protein composed of carbon, hydrogen, oxygen, nitrogen and sulphur. The core of the cell differs from protoplasm merely by the presence of phosphorus, which is generally oval.
  • Age of trees for felling: Good trees for felling vary from 50 to 100 years.
  • The season for felling: In autumn and spring, the sap is in vigorous motion; hence, the felling of trees in these seasons should be avoided. Mid-summer would be the proper season for felling in hilly areas as there is heavy rainfall in winter. For plain areas, mid-winter would be the proper season for felling as in summer, water contained in sap would be easily evaporated, forming cracks.

Defects in Timber

Defects in timber affect its strength, durability and other quality parameters. Due to defects in timber, it may not be useable for particular use. Defects occurring in timber are grouped into the following five divisions.

  1. Defect Due to Conversion
    1. Chip mark
    2. Diagonal grain
    3. Torn grain
    4. Wane
  2. Defects Due to Fungi
    1. Blue Stain
    2. Brown Rot
    3. Dry Rot
    4. Heart rot
    5. Sap Stain
    6. Wet Rot
    7. White Rot
  3. Defects Due to Insects
    1. Beetles
    2. Marine Borers
    3. Termites
  4. Defects Due to Natural Forces
    1. Burls
    2. Callus
    3. Chemical stain
    4. Coarse grain
    5. Dead wood
    6. Druxiness
    7. Foxiness
    8. knots
    9. Rind galls
    10. Shakes
    11. Twisted fibres
    12. Upsets
    13. Water stain
    14. Wind cracks
  5. Defects Due to Seasoning
    Follow defects occur in the seasoning process of wood.
    1. Bow
    2. Case-hardening
    3. Check
    4. Collapse
    5. Cup
    6. Honey-combing
    7. Radial shakes
    8. Split
    9. Twist
    10. Warp

Preservation of Timber

Preservation of timber is carried out to achieve the following three objectives:

  • To increase the life of timber structures
  • To make the timber structures durable, and
  • To protect the timber structures from the attack of destroying agencies such as fungi, insects, etc.

Requirements of a Good Preservative

  • It should allow decorative treatment on timber after being applied over the timber surface.
  • It should be capable of covering a large area with a small quantity.
  • It should be cheap and easily available.
  • It should be free from unpleasant smells.
  • Its penetrating power into wood fibres should be high. It is necessary for the preservative to be effective in penetrating at least a depth of 6 mm to 25 mm.

Types of Preservatives

  1. Ascu Treatment
    • Ascu is a special preservative which is developed at the Forest Research Institute, Dehradun. Its composition is as follows.
    • X-Part by weight of hydrated arsenic pentoxide (As2O5.2H2O).
    • Y-Part by weight of blue vitriol or copper sulphate (CuSO4.5H2O).
    • Z-Part by weight of potassium dichromate (K2Cr2O7) or sodium dichromate (Na2Cr2O7.2H2O)
    • This preservative gives timber protection against the attack of white ants. The surface treated with this preservative can be painted, polished, varnished or waxed.
  2. Chemical Salts
    • These are water-borne preservatives, and they are mostly salts dissolved in water. The usual salts are copper sulphate, mercury chloride, sodium fluoride and zinc chloride.
    • These preservatives are odourless and non-inflammable.
  3. Coal Tar
    Its cheapness and effective resistance. Coal tar increases protection against the penetration of water and fire. But the aesthetic value of timber decreases.
  4. Creosote oil
    In this case, the timber surface is coated with creosote oil.
  • Creosote oil is one of the best antiseptics. It is a black or brown liquid, weakly affected by water, neither volatile nor hygroscopic, harmless to wood or metal, inflammable, with an unpleasant odour and having the low wood-penetrating ability to the extent of 1 mm to 2 mm only.
  • Creosote oil should not be used for interior surfaces of dwelling houses, foodstuff-storage premises, underground installations and near inflammable surfaces.
  1. Oil Paints
    • The timber surface is coated with 2 or 3 coats of oil paint.
    • The wood should be seasoned; otherwise, sap will be confined and lead to timber decay.
    • The oil paints preserve the timber from moisture and make it durable.
  2. Solignum Paints
    • These paints preserve the timber from white ants as they are highly toxic in nature.
    • They can be mixed with colour pigment and applied in the hot state with the help of a brush.
    • The timber surface may therefore be given the desired colour or appearance.

Method for Preservation

There are six Methods Adopted for the Preservation of Timber:

  1. Brushing
    • The solution prepared from preservative is applied on timber surfaces by good quality brushes.
    • This is the simplest method and is generally adopted for seasoned timber.
    • The crocks should be filled up before the application of the preservative.
  2. Charring
    • The surface to be charred is kept wet for about half an hour, then burnt to a depth of about 15 mm over a wood fire.
    • The charred portion is then cooled with water.
    • Due to burning, a layer of coal is formed on the surface.
    • This layer is not affected by moisture, and white ants or fungi do not attack it.
    • The disadvantages of this method are:
      (i) The charred surface becomes black in appearance, so it cannot be used for exterior work.
      (ii) There is some timber strength loss as the cross-section is reduced due to charring.
  3. Dipping and Steeping
    • In this method, the timber to be given preservative treatment is dipped or soaked for a short period in the solution of the preservative.
    • This method gives slightly better penetration of preservatives than in the case of brushing or spraying.
  4. Hot and Cold Open Tank Treatment
    • In this method, the timber is submerged in a tank containing a solution of preservative, which is heated for a few hours at a temperature of 85℃ – 95℃.
    • The tank is then allowed to cool down gradually while submerging the timber.
    • This method is effective in giving protection to sapwood.
  5. Injecting Under Pressure
    This method is essential for treating non-durable timbers, which are to be used in places in danger of attack by fungi and insects.
  6. Spraying
    • In this method, the preservative solution is filled in a spraying pistol and then applied on a timber surface under pressure.
    • This method is also quite effective, and it is superior to brushing.

Fire Resistance of Timber

  1. Application of Special Chemicals
    • Two coats of solution of borax or sodium arsenate with a strength of 2 per cent are quite effective in rendering the timber fire-resistant.
    • When the temperature rises, they either melt or give off gases that hinder or forbid combustion.
  2. Sir Abel’s Process
    In this process, the timber surface is cleaned and coated with a dilute solution of sodium silicate. A cream-like paste of slaked fat lime is applied, and a concentrated solution of silicate of soda is applied to the timber surface.

Seasoning of Timber

  1. Object of Seasoning
    • To allow timber to burn readily if used as fuel.
    • To decrease the weight of timber and thereby lower the cost of transport and handling.
    • To make timber safe from the attack of fungi and insects.
    • To reduce the tendency of timber to crack, shrink and warp.
    • Make timber fit for receiving treatment of paints, preservatives, and varnishes.
    • To import hardness, stiffness, strength and better electrical resistance to timber.
  2. Methods of Seasoning

(a) Natural Seasoning

In this method, the seasoning of timber is carried out by natural air; hence, it is sometimes referred to as air seasoning.


  • Depending upon the climatic conditions, the moisture content of the ward can be brought down to about 10-20%
  • It does not require skilled supervision.
  • This method of seasoning timber is cheap and simple.
  • Providing artificial seasoning to timber sections thicker than 100 mm is uneconomical, as such sections dry very slowly.


  • As the process depends on the natural air, it sometimes becomes difficult to control.
  • The drying of the different surfaces may not be even and uniform.
  • If ends of thick timber sections are not projected by suitable moisture-proof coating, there are chances for end splitting.

(b) Artificial Seasoning

  • Following are the reasons for adopting artificial seasoning to natural seasoning.

A. The defects such as shrinkage, cracking and warping are minimized.

B. The drying is controlled, and there are practically no chances for the attack of fungi and insects.

C. The drying of the different surfaces is even and uniform.

D. It considerably reduces the period of seasoning.

E. There is better control of the circulation of air, humidity and temperature.

  1. Boiling
    In this method of artificial seasoning, timber is immersed in water and water is then boiled. But it affects the elasticity and strength of wood.
  2. Chemical seasoning
    This is also known as salt seasoning. In this method, timber is immersed in a solution of suitable salt. It is then taken out and seasoned ordinarily.
  3. Electrical seasoning
    • This method, use is made of high-frequency alternating currents.
    • This is the most rapid method of seasoning.
    • Due to high costs, this method is uneconomical.
  4. Klin Seasoning
    • In this method, timber drying is carried out inside an airtight chamber or oven.
  5. Water Seasoning
    • Timber pieces are immersed wholly in water, preferably in the running water of a stream. Care should be taken to see that timber is not partly immersed.
    • Timber is taken out after a period of about 2 to 4 weeks. During this period, sap contained in timber is washed away by water.

What is Lime?

lime is a building material used to construct various civil engineering works. It can also be used as the binding material for the construction of masonry structures.

Some Basic Definitions

  1. Calcination: The heating of limestone to redness in contact with air is known as the calculation.
  2. Hydraulicity is the property of lime by which it sets or hardens in damp places, water or thick masonry walls where there is no free air circulation.
  3. Quick Lime: The lime obtained by calcinating comparatively pure limestone is known as quick lime or caustic lime. It can slake with water and has no affinity for carbonic acid.
    • Its chemical composition is (CaO) oxide of calcium and has a great affinity for moisture.
    • As it comes out from kilns, the quick lime is known as the lump lime.
  4. Setting: The process of hardening lime after it has been converted into paste form is known as the setting. It is quite different from mere drying.
  5. Slaked Lime The product obtained by slaking of quick lime is known as the slaked lime or hydrate of lime. It is in white powder, and its chemical composition is Ca(OH)2 or hydrated oxide of calcium.


  1. Slaking: A chemical reaction occurs when water is added to the quick lime in sufficient quantity.
    • Due to this chemical reaction, the quick lime cracks swell and fall into a powder form called the calcium hydrate Ca (OH)2, known as the hydrated lime.
    • This process is known as slaking.

Classification of Limes

  1. Fat Lime: This lime is also known as high-calcium lime. Pure Lime, rich lime or white lime. It is popularly known as the fat lime as it slakes vigorously, and its volume is increased to about 2-2-5 times that of quick lime. The percentage of impurities in such limestone is less than 5%.
  2. Hydraulic Lime: This is known as water lime as it sets underwater. It contains clay and some amount of ferrous oxide. Hydraulic lime is divided into three types depending on the percentage of clay present.
    1. Feebly hydraulic lime
    2. Moderately hydraulic lime
    3. Eminently hydraulic lime

The hydraulic lime can be set underwater and in thick walls without free air circulation.

  1. Poor Lime: This lime is also known as impure or lean lime. It contains more than 30% of clay. It slakes very slowly.

Impurities in Limestones

  1. Magnesium carbonate
    • The magnesium limestones are hard, heavy and compact in texture.
    • The magnesium limestones display irregular properties of calcination, slaking and hardening.
    • Up to 5% of magnesium oxide imparts excellent hydraulic properties to the lime.
  2. Clay
    • It is mainly responsible for the hydraulic properties of lime.
    • The percentage of clay used to produce hydraulicity in time stone usually varies from 10 to 30.
    • Limes containing 3-5 per cent of clay do not display any hydraulic properties and do not set and harden underwater.
  3. Silica: In its free form, it has a detrimental effect on the properties of lime.
  4. Iron Compounds
    • Iron occurs in small proportions as oxides, carbonates and sulphides.
    • Pyrite or iron sulphide is regarded to be highly undesirable.
    • For hydraulic limes, 2-5 per cent of iron oxide is necessary.
  5. Sulphates: Sulphates, if present, slow down the slaking action and increase the setting rate of limes.
  6. Alkalis: When pure lime is required, the alkalis are undesirable. However, up to 5 per cent of alkalis in hydraulic lime do not have any ill effects.

What is Mortar?

Mortar is also a building material that can be used for the construction of civil engineering construction works. It is used as the binding material for masonry structures. The constituents of mortar can be mixed with a fixed proportion. based on their proportion, the strength and other properties of mortar depend.

Some Basic Definition

  • Building mortar is defined as a mixture of cement, sand and water.
  • Mortar is similar to concrete, but it does not contain coarse aggregate.
  • Mortars fill joints as a binder in stone and brick masonry.

Bulking of Sand

  • In the case of aggregates, there is another effect of the presence of moisture, viz. bulking, which is an increase in the volume of a given mass of sand (fine aggregate) caused by the films of water pushing the sand particle apart. For moisture content of about 5-8%, this volume increase may be as much as 20-40% depending upon the grading of the sand.
  • The finer the materials, the more the volume increase for the given moisture content.

Classification of Mortars

  • Mortars are classified based on the following:
  • Bulk density
  • Kind of binding materials
  • Nature of application
  • Special mortars

Properties of Good Mortar Mix and Mortar

The important properties of a good mortar mix are mobility, place ability and water retention.

  • Mobility
  • It indicates the consistency of the mortar mix, which may range from stiff to fluid.
  • The mobility of mortar mix depends on the compositions of mortar, and the mortar mixes used for masonry work are made sufficiently mobile.
  • Placeability
  • The placeability of the mortar mix should be such that a strong bond is developed with the bed’s surface.

Properties of a Good Mortar

  • It should be capable of developing good adhesion with the building units such as bricks, stones etc.
  • It should be capable of developing the designed stresses.
  • It should be cheap
  • It should be durable.
  • It should be easily workable.
  • It should be set quickly so that speed in construction may be achieved.

Uses of Mortar

  • To bind the building units such as bricks and stones.
  • To carry out pointing and plasterwork on exposed surfaces of masonry.
  • To form an even and soft bedding layer for building units.
  • To form joints of pipes.
  • To hide the open joints of brickwork and stonework.
  • To improve the general appearance of the structure.

Functions of Sand in Mortar

  1. Bulk
  2. Setting
  3. Shrinkage
  4. Strength

Tests for Mortars

  1. Adhesiveness to Building Units: Mortar is placed to join them to form a horizontal joint. If the size of the bricks is 19 cm x 9 cm x 9, a horizontal join of 9 cm x 9 cm = 81 cm2 will be formed. The ultimate adhesive strength of mortar per cm2 area is obtained by dividing the maximum load by = 81 cm2 area.
  2. Crushing Strength: Brick masonry or stone masonry laid in mortar to be tested is crushed in a compression machine. The load at which the masonry crushes gives the crushing strength
  3. Tensile Strength: The briquettes are tested in a tension testing machine. The cross-sectional area of the central portion is 38 mm x 38 mm or 1444 mm2 or 14.44 cm2.
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